[ARC5] 24vdc power

[Bob kb8tq]

Hi

Every so often one will find a switcher that is not “happy” 
with a voltage on the output when the input is un-powered.
This is not common, but it is worth thinking about. A series
diode (with an adequate current capacity / heatsink )  
typically takes care of the issue. 

One way to be sure the device is happy with a battery is
to use a 24V battery charger. Not cheap for a good one, 
maybe has RFI issues. The switcher could be an RFI source
as well. 

Either way, best to work things out before the next power
outage. Looking for that burning smell in the dark is not
a lot of fun …. 

Bob

> On Sep 4, 2022, at 12:06 PM, scottjohnson1 at cox.net wrote:
> 
> I wish I saved my old posts on this subject since it comes up every so
> often!  I find the best way to operate rotating machinery that once operated
> in a mobile environment is to replicate that environment.  SO-
> Get a power supply that can handle the full load current and float an SLA
> battery across it.  Size of the battery and power supply is proportional to
> load, but in your case, a 10-20 A switcher. Set to27.5 V (for normal indoor
> ambient temperature)
> Less for hotter, more for cooler, but in the range of 27-28V.  For your 10A
> load, 12V 7AH SLA batteries would do nicely. (Two in series).  Increase AH
> capacity proportionately for higher current loads.  Amazon and eBay have
> plenty of inexpensive switcher that will work, just don't buy the REALLY
> cheap ones, unless you like the acrid smell of burning components.
> 
> -----Original Message-----
> From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> On Behalf
> Of Charles via ARC5
> Sent: Sunday, September 4, 2022 10:23 AM
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] 24vdc power
> 
>> Hey guys,
>> What's everybody using to provide 24vdc for your military radios? Two
> 12vdc supplies in series?  Home brew?  Do they make a 24vdc switching supply
> that will handle 10 amps or so?
>> Thanks for your input,
>> 
>> Richard kn7sfz
> Anything with a dynamotor needs about five times the motor nameplate current
> for the starting surge...
> 
> I got a 2 KVA three-phase 115V 400 Hz rotary converter at a flea market but
> nothing I had was big enough to start it (rated at 27.5VDC at 115 amps!)
> 
> So I bought a 20 VAC, 5 KVA toroid transformer on ebay, a BFBR (big bridge
> rectifier), heat sink, a 220,000 uF cap, meters and shunts, and brewed up a
> 24-28V 120 amp brute force supply with 240 VAC input. THAT starts the
> converter all right. It doesn't even blink at smaller dynamotors :)
> 
> -Charles, WB3JOK/0
> 
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